High frequency pneumatically actuated drilling hammer

ABSTRACT

A drilling hammer in which a hammer piston in a cylinder is propelled in opposite directions by compressed air to impact repeatedly upon an anvil connected to a drill bit. On its return stroke, the hammer piston impacts against a spring device, storing energy therein which is returned by the spring device to the piston on its downstroke, the spring device causing the frequency of reciprocation of the hammer piston to increase considerably, correspondingly increasing the power output of the drilling hammer. Preferably, the spring device comprises a stack of Belleville springs or spring discs, which are more efficient in operation and which result in a more compact drilling hammer.

United States Patent Curington [4 1 Sept. 19, 1972 1541 HIGH FREQUENCY PNEUMATICALLY 3,480,088 11/1969 Ghelfi ..1 73/1 38 ACTUATED DRILLING HAMMER 3,606,930 9/1971 Curington ..173/136 Alfred R. Curington, Houston, Tex.

Baker Oil Tools, Inc., Los Angeles County, Calif.

Filed: Dec. 23, 1970 App1.No.: 100,887

Inventor:

Assignee:

US. Cl. ..173/ll9, 173/136, 175/296 Int. Cl. ..E2lb l/06 Field of Search ..173/l19, 120,121,136, 137,

References Cited UNITED STATES PATENTS 5/1960 Kurt ..173/139 12/1951 Topanelian, Jr ..175/296 12/1953 Topanelian, Jr 1 75/296 3/1966 Hazen et a1 ..175/296 Primary Examiner-James A. Leppink Attorney-Bernard Kriegel and Kendrick, Subkow & Kriegel [57] ABSTRACT A drilling hammer in which a hammer piston in a cylinder is propelled in opposite directions by compressed air to impact repeatedly upon an anvil connected to a drill bit. On its return stroke, the hammer piston-impacts against a spring device, storing energy therein which .is returned by the spring device to the piston on its downstroke, the spring device causing the frequency of reciprocation of the hammer piston to increase considerably, correspondingly increasing the power output of the drilling hammer. Preferably, the spring device comprises a stack of Belleville springs or spring discs, which are more efficient in operation and which result in a more compact drilling hammer.

15 Claims, 8 Drawing Figures HIGH FREQUENCY PNEUMATICALLY ACTUATED DRILLING HAMMER The present invention relates to drill bit apparatus for drilling a hole in a formation, and more particularly to pneumatically operated drilling apparatus that imparts a percussive action to a drill bit.

Compressed air operated drilling hammers are known, in which the compressed air operates alternately on opposite ends of a hammer piston to reciprocate it in'a companion cylinder and cause it to repeatedly impact against an anvil suitably secured to a drill bit. The hammer piston is shifted on its upstroke by-compressed air, which is shut off before the top of the stroke is reached, the energy in the piston continuing its upward movement, the piston compressing the air, which brings it to a halt. On the downstroke, the energy in this compressed air isreturned to a substantial extent to the piston, which is available for adding to the impact blow imparted to the anvil at the end of the piston downstroke. The distance the piston must travel in compressing the air on its up or return stroke, and the same distance it must travel on its power or downstroke, require the consumption of considerable time, lowering the frequency of operation of the piston to a substantial extent, and, therefore, substantially decreases the power output of the drilling hammer.

By virtue of the present invention, the frequency of operation of a hammer piston is increased considerably by reducing the travel requirement of the hammer piston in its confining cylinder; that is to say, both the upstroke and downstroke of the hammer piston are decreased. The air above the piston is compressed by the piston as a result of its upward travel in the cylinder on its return stroke, such air expanding and assisting in propelling the piston downwardly on its down or hammer stroke, so that very little energy is actually lost. In its upstroke, the frequency could be increased by causing the hammer position to impact against a solid member, such as the upper head of itsconfining cylinder, but such impact blows would have the disadvantage of excessively tightening the joints of the drill stringto which the drilling hammer is secured and could cause fatigue failure in parts of the apparatus.

With the present invention, a substantial frequency increase is achieved by causing the piston hammer to impact against a yieldable member, such as a spring device, on its upstroke. The energy absorbed by the spring in bringing the hammer piston to rest is returned to the piston on its downstroke, the rate of reciprocation of the hammer piston being thereby increased without producing the undesirable results incident to the impacting of the hammer piston on a solid member on its up or return stroke. Moreover, in the present invention, the hammer piston is caused to impact against This invention possesses many other advantages, and has other purposes which may be made more clearly apparent from a consideration of a form in which it may be embodied. This form is shown in the drawings accompanying and forming part of the present specification. It will now be described in detail, for the purpose of. illustrating the general principles of the invention; but it is to be understood that such detailed description is not to be taken in a limiting sense.

Referring to the drawings:

FIGS. la, 1b and 10 together constitute a longitudinal section through an apparatus embodying the invention, with parts in their relative position after the hammer piston has completed delivering an impact blow against its companion anvil and the drill bit secured thereto, FIGS. lb and 10 being lower continuations of FIGS. la and 1b, respectively;

FIGS. 2a and 2b are views similar to FIGS. la-lc, with the hammer piston in its upper position, FIG. 2b being a lower continuation of FIG. 2a;

FIG. 3 is an enlarged cross-section taken along the line 3-3 on FIG. 1c;

FIG. 4 is an enlarged partial cross-section taken along the line 4-4 on FIG. 10;

FIG. 5 is an enlarged cross-section taken along the line 55 on FIG. 1b.

The down-hole drilling hammer A illustrated in the drawings is connected to the lower end of a string of drill pipe B extending to a drilling; rig (not shown) at the top of a bore hole C being drilled, and by means of which the apparatus and a drill bit D at its lower end are rotated while compressed air, or other suitable fluid medium, is pumped down the drill pipe for operating the apparatus. The drill bit D is of any suitable type and may have sintered tungsten carbide inserts (not shown) mounted in its end face for impacting against the bottom F of the bore hole while the apparatus A and bit D are being rotated, to impart a drilling action against the full area of the bottom of the hole as a result of the im pacting action imparted to an anvil l0 disclosed as integral with the drill bit, although the drill bit may be connected to the anvil in any other suitable manner.

The drilling hammer apparatus A includes an outer elongate housing structure 11 made of several sections or components, including an upper section 12 threadedly secured to an upper sub 13 having an upper threaded box 14 for attachment to the lower pin 15 of an adjacent drill pipe section B. The lower end of the upper section 12 is threadedly secured to an intermediate coupling section 16 which is, in turn, threadedly attached to a lower housing section 17, the lower end of which is threadedly secured to a lower sub 18 integral with a lower cylinder sleeve 19 extending upwardly therefrom and spaced laterally from the housing to form an annular exhaust passage 20 therewith. Upper radial exhaust ports 21 extend through the upper portion of the cylinder sleeve, establishing communication between the interior of the sleeve and the exhaust passage 20; whereas, lower generally radial exhaust ports 22 extend through the sleeve, establishing communication between the exhaust passage 20 and the interior of the sleeve 19. The upper portion of the lower sleeve carries a suitable side seal ring 23 thereon sealing against the inner wall 24 of the lower housing section 17 immediately above the annular exhaust passage 20.

An upper cylinder sleeve 25 is integral with and extends downwardly from the intermediate coupling section 16 within the lower housing section 17, being laterally spaced therefrom to provide a high pressure annular air passage 26 therebetween. The lower end of this sleeve 25 carries a suitable side seal ring 27 sealing against the wall 24 of the lower housing section, the cylinder sleeve having a plurality of lower radial inlet ports 28 establishing communication between the high pressure air passage 26 and the interior of the upper sleeve, and also having upper ports 29 establishing communication between the upper end of the annular passage 26 and the lower end of an annular inlet passage 30 formed between an inner tubular member or sleeve 31 having a head 32 engaging the inner wall 33 of the upper sleeve below its ports 29, and sealed thereagainst by a suitable elastomer head seal 34 also engaging the wall of the sleeve 25. The tubular member 31 is elongate, extending upwardly through the coupling 16 and to the upper portion of the upper housing section 12, encompassing a lower head 35 of the upper sub 13, against which it is sealed by a suitable elastomer side seal member 36 on the head engaging the wall 37 of the inner tubular member 31.

Compressed air pumped downwardly through the tubular string B can enter a central passage 38 through the upper sub, which communicates with side ports 39 in the sub opening into the upper end of the annular inlet passage 30, such air being capable of passing through the upper ports 29 in the upper cylinder-sleeve 25 into the high pressure passage 26, and then through the inlet ports 28 at the lower portion of the sleeve 25 It is to be noted that the upper and lower cylinder sleeves 25, 19 are longitudinally spaced from one another to a substantial extent, allowing a cylinder portion 40 of the lower housing section to be provided therebetween of a substantially greater inside diameter than the inside diameters of the upper and lower cylinder sleeves, discharge or exhaust ports 41a extending through the larger diameter cylinder 40 and establishing communication between its interior and the exterior of the housing 11.

A hammer piston 41 is reciprocable within the upper and lower cylinders 2 5, 19 and the intermediate, larger diameter cylinder member 40 therebetween. This piston includes an upper piston portion 42 slidable longitudinally in the upper cylinder sleeve 25, a lower piston portion 43 slidable longitudinally in the lower cylinder sleeve 19, and an enlarged intermediate piston portion 44 integral with such upper and lower piston portions and slidable along the inner wall 24 of the enlarged cylinder. The piston 41 is adapted to be shifted downwardly to deliver an impact blow against the upper impact head 45 of the anvil 10 mounted within the lower cylinder sleeve 19 and lower sub 18, this anvil being integral with the drill bit D, or otherwise suitably secured thereto. The anvil makes a spline connection with the lower sub 18, to permit longitudinal movement of the anvil and bit with respect to the lower sub 18, and also to enable the rotary motion of the drill pipe B to be transmitted through the upper sub 13 and housing 11 to the lower housing sub 18, and then to the anvil l and drill bit D. As specifically shown, the anvil connection is provided by inwardly extending circumferentially spaced splines 46 on the lower sub slidably meshing with companion splines 47 on the anvil.

When the drill bit D engages the bottom F of the hole and the housing 11 and its lower sub 18 are disposed in a downward position with respect to the anvil and bit, as determined by engagement of the lower end 18a of the lower sub with an upwardly facing shoulder 10a on the anvil, the impact head 45 is disposed within the lower cylinder sleeve 19 above its ports 22, making a close fit therewith. At this time, when the piston 41 has been disposed in its uppermost position within the housing and sleeves 25, 19 (FIGS. 2a, 2b), compressed air can exhaust through the upper ports 21 into the exhaust annulus 20, and then through the lower ports 22 to the interior of the sleeve 19, such air continuing to flow through inlet ports 50 in the upper portion of the anvil into its central passage 51, discharging through lower nozzles or passages 52 in the drill bit against the bottom F of the bore holeC to clean the bottom of cuttings, clean the bit D, and convey such cuttings around the drill bit and upwardly through the annulus surrounding the housing 11, and the annulus surrounding the drill pipe B to the top of the bore hole. The upper end of the central passage 51 is closed by a suitable plug 53.

The lower piston portion 43 has suitable seal means on its periphery for sealing against the inner wall of the lower cylinder sleeve. As illustrated, such seal means may take the form of a labyrinth seal provided by a series of circumferential external grooves 54 in the piston in which air will be trapped. When the piston is in its lowermost position against the impact head, the seals 54 extend from a location above the lower exhaust ports 22 to a location above the upper exhaust ports 21. The piston has a longitudinal hammer return passage 55 extending therewithin from its lower end and into communication with an upper annular inlet groove 56, which will be in registry with the inlet ports 28 when the hammer piston is in its lowermost position (FIGS. la-lca). The piston also has a longitudinal impact passage 57 in its upper small diameter portion extending from the upper end of the piston and communicating with an elongate lower side port 58 which opens into the annular space 59 between the small diameter piston 42 and the enlarged cylinder 40 when the piston is in its lower position. The small diameter upper piston portion 42 has suitable seal means 60 thereon on opposite sides of its inlet groove 56 which can assume any desirable form. As shown, labyrinth seal grooves 60 are provided capable of trapping air and sealing against the inner wall of the upper cylinder sleeve 25.

The enlarged intermediate piston portion 44 slidably seals against the wall 24 of the enlarged cylinder 40. This intermediate piston portion carries an upper seal ring 61, such as a piston ring, therein near its upper portion and a lower piston ring 62 at its lower portion, so as to prevent leakage along the enlarged hammer piston portion 44.

When the hammer piston 41 is in its lowermost position, as illustrated in FIGS. 1b and 1c, the lower piston portion 43 closes the upper exhaust ports 21, but its upper annular groove 56 is aligned with the inlet ports. 28, its labyrinth seals 60 being disposed on opposite sides of the latter. The enlarged piston portion 44 seals against the enlarged cylinder 40 below the discharge ports 41a. When the piston is in the position illustrated in FIGS. lb and 1c, air in the cylinder space or chamber 65 within the upper tubular member 31 and in the upper cylinder sleeve 25 abovethe piston will have exhausted through the impact passage 57 and its side port 58 into the enlarged cylinder 40, and through its discharge or exhaust ports 41a into the bore hole surrounding the apparatus. At this time, compressed air can pass from the inlet ports 28 into the annular groove 56, and then into the hammer return passage 55 to its lower end, acting upon the lower end area of the smaller diameter piston 43 to shift the piston 41 upwardly in the housing and the cylinder sleeves away from the anvil 10. Such air under pressure can also pass through side port 66 communicating with the return hammer passage 55 into the annular space 660 above the lower cylinder sleeve 19 and below the enlarged piston portion 44, acting on the annular area S of the hammer piston and assisting in shifting the piston to its upperposition.

The hammer piston moves only a short distance on its upward or return stroke beforethe labyrinth seals 60 below its annular groove 56 close the inlet ports 28, the compressed air introduced through the hammer return passage 55 continuing to expand, driving the hammer piston 41 upwardly until its upper end impacts against a lower spring seat 70 engaged by a plurality of spring discs 71, such as Belleville springs, the upperendof which bearagainst the lower head 32 of the upper tubular member 31, which functions as an upper spring seat. The kinetic energy in the hammer piston 41 is transferred to the springs 71, and also to the air trapped in the chamber 65 above the piston, which it is compressing.

Near the top of the hammerpistonstroke, the impact passage side port 58 is placed in communication with the inlet ports 28, the seal ring 61 on the enlarged piston portion 44 sealing'against the enlarged cylinder wall 24 above the discharge ports 41a, and the labyrinth seals 60 above the side port 58 sealingly engaging the upper cylinder sleeve 25 above the inlet ports 28 (FIG. 2a). As a result, compressed air flows from the annular passage 30 through the ports 28 into the impact passage 57 to the upper end of the piston 41, forcing the pistondownwardly, aided by the energy stored in the Belleville springs 71 and the compressed air in the cylinder space 65. Because of the large length and volume of the cylinder space, a large quantity of air under pressure is introduced through the impact passage 57 into the chambers 65, such compressed air shifting the hammer piston 41 downwardly, the inlet ports 28 being closed off after a relatively short downward movement of the piston, because of the sealing action of the labyrinth seals 60 against the wall of the upper cylinder sleeve 25 below the inlet ports 28. However, the compressed air above the piston expands and propels the hammer piston 41 downwardly, causing it to impact against the anvil head 45, such impact blow being delivered through the drill bit D to the bottom F of the bore hole. During the downstroke of the hammer piston 41, when the upper seal 61 on the enlarged hammer piston portion 44 moves below the discharge ports 410, the air above the impact piston can exhaust through the impact passage 57, its side port 58, and the housing discharge ports 41a into the annulus surrounding the housing 11, to convey the cuttings upwardly around the apparatus and through the annulus surrounding the string of drill pipe B to the top of t the bore hole.

immediately prior to the hammer piston impacting against the anvil head 45, the annular piston groove 56 moves into communication with the inlet ports 28, the compressed air passing through the return passage 55 to the bottom of the piston and into the annular space below the enlarged piston portion 44, to return the piston 41 to its upper position. The foregoing cycle is then repeated. t

It should be noted that when the hammer piston 41 is at the upper end of its stroke, itsllower end is disposed above the upper. exhaust ports 21 in the lower cylinder sleeve 19, (FIG. 2a, 2b), allowing the compressed air in the lower cylinder sleeve 19 below the piston and in the annular space 66a to pass through the upper exhaust ports 21 into the annular exhaust passage 20, from where the air will flow through the lower ports 22 into the anvil passage 50, 51, and then out through the bit nozzles 52 to clean the bottom .F of cuttings and to maintain the drill bit in a clean and cool condition.

The area available over which the compressed air acts on the downstroke or power stroke of the piston is the full cross-sectional area of the small diameter upper piston portion 42 plus the annular area S of the intermediate piston portion 44 between the small diameter piston portion and the wall 24 of the large cylinder 40. In other words, the annular area available for delivery on the power stroke is the full cross-section area of the enlarged intermediate piston portion 44, or the area acrossthe inner wall 24 of the larger cylinder. A corresponding area is available for propelling the hammer piston 41 upwardly on its return stroke. The large areas over which compressed'air can act is much greater than would be available if the hammer piston were made of a uniform diameter throughout its length, in view of the restrictions imposed within the housing by the upper and lower cylinder sleeves 25, 19. Because of the availability of the much greater piston area on which the compressed air can act, more power is imparted to the piston, such that even when relatively low air pressures only are available, sufficient kinetic energy can be imparted to the piston to cause it to deliver an effective impact blow upon the anvil 10 and the bit D attached thereto. In addition to the larger piston area that is provided in the apparatus, the large volume of the cylinder space or chamber 65 above the piston permits the introduction of more high pressure air into the apparatus for action upon the piston on its downstroke, permitting more power to be developed, since the compressed air does not reduce in pressure to as great an extent during the downstroke of the hammer piston and before the air can exhaust through the ports 41a.

The discharge of the compressed air upon the downstroke of the hammer piston through the discharge ports 41a provides a direct travel path for the air into the bore hole for lifting the cuttings to the top of the hole, such air being provided in a comparatively large volume. Such air need not traverse a circuitous path, as is necessary for the compressed air below the piston 41 to follow at the end of the piston upstroke, which enhances the efficiency of the apparatus. Particularly in air hammers of small size, thedirect exhaust of the power air into the annulus surrounding the apparatus insures a sufiicient air volume for carrying the sures a rapid escape of the power air and, therefore,

results in less air being trapped in the cylinder 25 and chamber 65 above the piston upon its upstroke, so that the piston on its upstroke need perform less work in compressing air trapped thereabove.

The apparatus illustrates the Belleville or annular,

tapered disc springs in which the energy of the hammer piston 41 is stored on its upstroke, and which returns the energy to the piston on its downstroke, the downward expansion of the stack of disc springs being limited by engagement of its lowerseat 70 with an upwardly facing shoulder 70a formed in the upper cylinder sleeve.

' The energy absorbing spring device70, 71 is engaged by the piston 41 on its upstroke, receivingthe energy therein, returning such energy to the piston on its downstroke. The distance travelled by the hammer piston 41 on its upstroke is reduced considerably over prior devices, in which the piston is brought to rest by compressing air in the cylinder space of chamber 65. Similarly, the piston is moved downwardly a lesser distance on its downstroke under the action of the compressed air acting on the upper small diameter piston 42 and the annular area S of the enlarged intermediate piston portion 44, downward movement of the piston being assisted by the expansion of the spring device 71. Thus, substantially all of the energy imparted to the spring'device by the piston on its upstroke is returned to the piston on its downstroke, the air compressed in the cylinder space or chamber 65 also assisting in driving the piston downwardly on its power stroke.

In view of the lesser distance of travel of thepiston 41 within the cylinders, both on its upstroke and its downstroke, a' significant increase in frequency of reciprocation of the piston has been achieved. With the use of the spring device, the frequency of operation and, therefore, the power output have been increased about 55 percent when compared with the performance of the same drilling hammer without the spring device embodied therein.

The impacting of the hammer piston 41 on the sprin device 71 on its upstroke has not only increased the frequency of its reciprocation and, therefore, the power delivered to the drill bit, but such desirable results have been achieved without any harmful effects being imposed on the apparatus or the drilling string attached to it. The frequency of reciprocation of the hammer piston could be increased if it were permitted to impact on its upstroke against a solid member, and the horsepower delivered would be correspondingly increased. However, the sudden arresting of the hammer piston on its upstroke by permitting it to effect a solid impact on the apparatus produces highly disadvantageous effects, such as excessive tightening of the drill string joints, increase of the stress cycles, etc. The absorption of the kinetic energy in the piston 41 through the spring device 71 eliminates such harmful effects, while still greatly increasing the frequency of operation of the hammer piston.

It is desirable to use the Belleville or disc spring pack, rather than a conventional coil or helical spring, which would also increase the frequency of operation of the hammer piston. The Belleville spring pack or stack is more compact than a coil spring, and, therefore, enables the apparatus to be made of a decreased length. Moreover, coil or helical springs have the disadvantage of being capable of transmitting reflective stresses, causing oscillation in the spring and its early failure from fatigue. A Belleville spring pack or stack cannot transmit reflected tensile stresses, and, therefore, cannot oscillate, the spring stack having a considerably longer useful life in the drilling hammer apparatus.

The apparatus is rendered inoperable unless the bit D is resting upon the bottom F of the hole C, with a required amount of drilling weight imposed upon it by the drill pipe B. When the drill pipe ,is elevated to raise the bit from the bottom of the hole, the anvil l0 andbit D drop downwardly, as permitted by the telescoping of the anvil 10 within the lower sub 18, untilan external anvil flange 80 engages a plurality of circumferentially spaced limit pins 81 extending through bores 82 in the lower sub 18 and held in an inward position by a depending skirt 83 of the lower housing section 17. Such lower positioning of the anvil permits the piston to drop downwardly within the upper and lower cylinder sleeves 25, 19 and intermediate large cylinder to a position determined by engagement of the enlarged piston portion 44 with the upper end of the lower cylinder sleeve 19, at which time the annular groove 56 of the piston still communicates with the inlet ports 28, the impact head being disposed in an enlarged internal diameter portion 84 of the lower cylinder sleeve, such that compressed air can be pumped through the apparatus and through the hammer return passage 55, discharging from the lower end of v the piston and passing around the impact head 45 for continued flow through the ports 50 into the central passage 51 of the anvil and out through the bit nozzles 52. With the parts in this position, compressed air can be pumped continuously through the apparatus to clean the bit D of cuttings and impart a circulating action upwardly through the annulus surrounding the apparatus A and the drill pipe B to the top of the bore hole. It is only when drilling weight is imparted to the drill bit, with the housing structure 11 telescoped downwardly over the anvil 10, to hold the drill bit D against the bottom F of the bore hole, that the apparatus becomes operative.

lclaim:

1. In percussion drilling apparatus: housing means operatively connectible to a drill string, said housing means including a cylinder; an anvil relatively reciprocable in said housing means and connectible to a drill bit; a hammer piston reciprocable in said cylinder for intermittently impacting against said anvil; means for directing a fluid medium under pressure into said cylinder alternately at upper and lower portions thereof for action upon said piston to reciprocate said piston in said cylinder; and arresting means in said housing means at the upper portion of said cylinder engaged by said piston at the upper end of its stroke to arrest and stop upward travel of said piston and force said piston downwardly in said cylinder toward the anvil, said arresting means providing a chamber containing the fluid medium and in which the fluid medium is compressible by said piston upon its upstroke.

end by said hammer piston to receive energy therefrom on the upstroke of said piston and to return such energy to said piston to force said piston downwardly in said cylinder. I

4. In apparatus as defined in claim I; said arresting means including an upper seat secured to said housing means, yieldable means bearing at its upper end against said seat and engaged at its lower end by said hammer piston to receive energy therefrom on the upstroke of said piston and to return such energy to said piston to force said piston downwardly in said cylinder.

5. In apparatus as defined in claim 1; said arresting means including an upper seat secured to said housing means, spring, means bearing at its upper end against said seat and engaged at its lower end by said hammer piston to receive energy therefrom on the upstroke of said piston and to return such energy to said piston to force said piston downwardly in said cylinder.

6. In apparatus as defined inclaim 1; said arresting means including an upper seat secured to said housing means, a spring device bearing at its upper end against said upper seat, a shiftable lower seat contacting the lower end of said spring device and engaged by said hammer piston to store energy in said spring device on the upstroke of said piston and to return such energy to said piston to force said piston downwardly in said cylinder, and stop means in said housing means engaged by said lower seat to limit its downward movement in said housing means.

7. In apparatus as defined in claim 1; said arresting means including spring means bearing at its upper end against said housing means and engaged at its lower end by said hammer piston to receive energy therefrom on the upstroke of said piston and to return such energy to said piston to forcesaid piston downwardly in said cylinder, said spring means comprising a stack of tapered spring discs.

8. In apparatus as defined in claim 1; said arresting means including an upper seat secured to said housing means, spring means bearing at its upper end against said seat and engaged at its lower end by said hammer piston to receive energy therefrom on the upstroke of said piston and to return such energy to said piston to force said piston downwardly in said cylinder, said spring means comprising a stack of tapered spring discs. 7

9. In apparatus as defined in claim 1; said arresting means including an upper seat secured to said housing means, a spring device bearing at its upper end against said upper seat, a shiftable lower seat contacting the lower end of said spring device and engaged by said hammer piston to store energy in said spring device on I the upstroke of said piston and to return such energy to said piston to force said piston downwardly in said cylinder, and stop means in said housing means engaged by said lower seat to limit its downward movement in said housing means, said spring device comprising a stack of tapered spring discs.

10. In percussion drilling apparatus; housing means operatively connectible to a drill string, said housing means including a cylinder; an anvil relatively reciprocable in said housing means and connectible to a drill bit; a hammer pistonreciprocable in said cylinder for intermittently impacting against said anvil; means for directing a gaseous medium under pressure into said cylinder alternately at upper and lower portions thereof-foraction upon said piston to reciprocate said piston in said cylinder; arresting means insaid housing means at the upper portion of said cylinder engaged by said piston at the upper end of. its stroke to arrest and stop upward travel of saidpiston and force said piston downwardly in said cylinder toward the anvil; said housing means having a chamber provided at least partly within said'arresting means and containing the gaseous medium and inwhich the gaseous medium is compressed by said piston upon upward movement of said piston in said cylinder.

11. In percussion drilling apparatus: housing means operatively connectible to a dril] string, said housing means comprising a cylinder; an anvil relatively reciprocable in said housing means and connectible to a drill bit; a hammer piston reciprocable in said cylinder for intermittently impacting against said anvil; means for directing a gaseous medium under pressure into said cylinder alternately at upper and lower portions thereof for action upon said piston to reciprocate said piston in said cylinder; arresting means in said housing means at the upper portion of said cylinder engaged by said piston at the upper end of its stroke to arrest and stop upward travel of said piston and force said piston downwardly in'said cylinder toward the anvil; said housing means having a chamber containing the gaseous medium and in which the gaseousmedium is compressed by said piston upon upward movement of said piston in said cylinder; said arresting means including spring means bearing at its upper end against said housing means and engaged at its lower end by said hammer piston to receive energy therefrom on the upstroke of said piston and to return such energy to said piston to force said piston downwardly in said cylinder; said chamber being above said arresting means.

12. In percussion drilling apparatus: housing means operatively connectible to a drill string, said housing means comprising a cylinder; an anvil relatively reciprocable in said housing means and connectible to a drill bit; a hammer piston reciprocable in said cylinder for intermittently impacting against said anvil; means for directing a gaseous medium under pressure into said cylinder alternately at upper and lower portions thereof for action upon said piston to reciprocate said piston in said cylinder; arresting means in said housing means at the upper portion of said cylinder en- 1 said piston in said cylinder; said arresting means including an upper seat secured to said housing means, spring means bearing at its upper end against said seat and engaged at its lower end by said hammer piston to receive energy therefrom on the upstroke of said piston and to return such energy to said piston to force said piston downwardly in said cylinder; said chamber being above said arresting means.

13. In percussion drilling apparatus: housing means operatively connectible to a drill string, said housing means comprising a cylinder; an anvil relatively reciprocable in said housing means and connectible to a drill bit; a hammer piston reciprocable in said cylinder for intermittently impacting against said anvil; means for directing a gaseous medium under pressure into said cylinder alternately at upper and lower portions thereof for action upon said piston to reciprocate said piston in said cylinder; arresting means in said said housing means having a chamber containing the gaseous medium and in which the gaseous medium is compressed by said piston upon upward movement of said piston in said cylinder; said arresting means including an upper seat secured, to said housing means, a spring device bearing at its upper end against said upper seat, a shiftable lower seat contacting the lower end of said spring device and engaged by said hammer piston to store energy in said spring device on the upstroke of said piston and to return such energy to said piston to force said piston downwardly in said cylinder, stop means in said housing means engaged by said lower seat to limit its downward movement in said housing means; said chamber being above said arresting means.

14. In apparatus as defined in claim 11, said spring means comprising a stack of tapered spring discs.

15. In apparatus as defined in claim 13, said spring device comprising a stack of tapered spring discs. 

1. In percusSion drilling apparatus: housing means operatively connectible to a drill string, said housing means including a cylinder; an anvil relatively reciprocable in said housing means and connectible to a drill bit; a hammer piston reciprocable in said cylinder for intermittently impacting against said anvil; means for directing a fluid medium under pressure into said cylinder alternately at upper and lower portions thereof for action upon said piston to reciprocate said piston in said cylinder; and arresting means in said housing means at the upper portion of said cylinder engaged by said piston at the upper end of its stroke to arrest and stop upward travel of said piston and force said piston downwardly in said cylinder toward the anvil, said arresting means providing a chamber containing the fluid medium and in which the fluid medium is compressible by said piston upon its upstroke.
 2. In apparatus as defined in claim 1; said arresting means including yieldable means bearing at its upper end against said housing means and engaged at its lower end by said hammer piston to receive energy therefrom on the upstroke of said piston and to return such energy to said piston to force said piston downwardly in said cylinder.
 3. In apparatus as defined in claim 1; said arresting means including spring means bearing at its upper end against said housing means and engaged at its lower end by said hammer piston to receive energy therefrom on the upstroke of said piston and to return such energy to said piston to force said piston downwardly in said cylinder.
 4. In apparatus as defined in claim 1; said arresting means including an upper seat secured to said housing means, yieldable means bearing at its upper end against said seat and engaged at its lower end by said hammer piston to receive energy therefrom on the upstroke of said piston and to return such energy to said piston to force said piston downwardly in said cylinder.
 5. In apparatus as defined in claim 1; said arresting means including an upper seat secured to said housing means, spring means bearing at its upper end against said seat and engaged at its lower end by said hammer piston to receive energy therefrom on the upstroke of said piston and to return such energy to said piston to force said piston downwardly in said cylinder.
 6. In apparatus as defined in claim 1; said arresting means including an upper seat secured to said housing means, a spring device bearing at its upper end against said upper seat, a shiftable lower seat contacting the lower end of said spring device and engaged by said hammer piston to store energy in said spring device on the upstroke of said piston and to return such energy to said piston to force said piston downwardly in said cylinder, and stop means in said housing means engaged by said lower seat to limit its downward movement in said housing means.
 7. In apparatus as defined in claim 1; said arresting means including spring means bearing at its upper end against said housing means and engaged at its lower end by said hammer piston to receive energy therefrom on the upstroke of said piston and to return such energy to said piston to force said piston downwardly in said cylinder, said spring means comprising a stack of tapered spring discs.
 8. In apparatus as defined in claim 1; said arresting means including an upper seat secured to said housing means, spring means bearing at its upper end against said seat and engaged at its lower end by said hammer piston to receive energy therefrom on the upstroke of said piston and to return such energy to said piston to force said piston downwardly in said cylinder, said spring means comprising a stack of tapered spring discs.
 9. In apparatus as defined in claim 1; said arresting means including an upper seat secured to said housing means, a spring device bearing at its upper end against said upper seat, a shiftable lower seat contacting the lower end of said spring device and engaged by said hammer piston to store energy in said spring devicE on the upstroke of said piston and to return such energy to said piston to force said piston downwardly in said cylinder, and stop means in said housing means engaged by said lower seat to limit its downward movement in said housing means, said spring device comprising a stack of tapered spring discs.
 10. In percussion drilling apparatus; housing means operatively connectible to a drill string, said housing means including a cylinder; an anvil relatively reciprocable in said housing means and connectible to a drill bit; a hammer piston reciprocable in said cylinder for intermittently impacting against said anvil; means for directing a gaseous medium under pressure into said cylinder alternately at upper and lower portions thereof for action upon said piston to reciprocate said piston in said cylinder; arresting means in said housing means at the upper portion of said cylinder engaged by said piston at the upper end of its stroke to arrest and stop upward travel of said piston and force said piston downwardly in said cylinder toward the anvil; said housing means having a chamber provided at least partly within said arresting means and containing the gaseous medium and in which the gaseous medium is compressed by said piston upon upward movement of said piston in said cylinder.
 11. In percussion drilling apparatus: housing means operatively connectible to a drill string, said housing means comprising a cylinder; an anvil relatively reciprocable in said housing means and connectible to a drill bit; a hammer piston reciprocable in said cylinder for intermittently impacting against said anvil; means for directing a gaseous medium under pressure into said cylinder alternately at upper and lower portions thereof for action upon said piston to reciprocate said piston in said cylinder; arresting means in said housing means at the upper portion of said cylinder engaged by said piston at the upper end of its stroke to arrest and stop upward travel of said piston and force said piston downwardly in said cylinder toward the anvil; said housing means having a chamber containing the gaseous medium and in which the gaseous medium is compressed by said piston upon upward movement of said piston in said cylinder; said arresting means including spring means bearing at its upper end against said housing means and engaged at its lower end by said hammer piston to receive energy therefrom on the upstroke of said piston and to return such energy to said piston to force said piston downwardly in said cylinder; said chamber being above said arresting means.
 12. In percussion drilling apparatus: housing means operatively connectible to a drill string, said housing means comprising a cylinder; an anvil relatively reciprocable in said housing means and connectible to a drill bit; a hammer piston reciprocable in said cylinder for intermittently impacting against said anvil; means for directing a gaseous medium under pressure into said cylinder alternately at upper and lower portions thereof for action upon said piston to reciprocate said piston in said cylinder; arresting means in said housing means at the upper portion of said cylinder engaged by said piston at the upper end of its stroke to arrest and stop upward travel of said piston and force said piston downwardly in said cylinder toward the anvil; said housing means having a chamber containing the gaseous medium and in which the gaseous medium is compressed by said piston upon upward movement of said piston in said cylinder; said arresting means including an upper seat secured to said housing means, spring means bearing at its upper end against said seat and engaged at its lower end by said hammer piston to receive energy therefrom on the upstroke of said piston and to return such energy to said piston to force said piston downwardly in said cylinder; said chamber being above said arresting means.
 13. In percussion drilling apparatus: housing means operatively connectible to a drill string, said housing means comprising a cylinder; an anvil relatively reciprocable in said housing means and connectible to a drill bit; a hammer piston reciprocable in said cylinder for intermittently impacting against said anvil; means for directing a gaseous medium under pressure into said cylinder alternately at upper and lower portions thereof for action upon said piston to reciprocate said piston in said cylinder; arresting means in said housing means at the upper portion of said cylinder engaged by said piston at the upper end of its stroke to arrest and stop upward travel of said piston and force said piston downwardly in said cylinder toward the anvil; said housing means having a chamber containing the gaseous medium and in which the gaseous medium is compressed by said piston upon upward movement of said piston in said cylinder; said arresting means including an upper seat secured to said housing means, a spring device bearing at its upper end against said upper seat, a shiftable lower seat contacting the lower end of said spring device and engaged by said hammer piston to store energy in said spring device on the upstroke of said piston and to return such energy to said piston to force said piston downwardly in said cylinder, stop means in said housing means engaged by said lower seat to limit its downward movement in said housing means; said chamber being above said arresting means.
 14. In apparatus as defined in claim 11, said spring means comprising a stack of tapered spring discs.
 15. In apparatus as defined in claim 13, said spring device comprising a stack of tapered spring discs. 